🐍 Python Basics

# This is my first Python program!
# Lines starting with # are comments (notes for humans)

print("Hello, World!")

# Output: Hello, World!

# Creating variables (putting stuff in boxes)

age = 25                  # Box named "age" holds number 25
name = "Alice"            # Box named "name" holds text "Alice"
height = 5.6              # Box named "height" holds decimal 5.6
is_student = True         # Box named "is_student" holds True/False

# Using the variables
print("Name:", name)
print("Age:", age)
print("Height:", height, "feet")
print("Is student?", is_student)

# Output:
# Name: Alice
# Age: 25
# Height: 5.6 feet
# Is student? True

# Different data types

my_age = 25                  # Integer (whole number)
my_height = 5.9              # Float (decimal number)
my_name = "John"             # String (text)
is_happy = True              # Boolean (True or False)

# Check what type a variable is using type()
print(type(my_age))        # Output: <class 'int'>
print(type(my_height))     # Output: <class 'float'>
print(type(my_name))       # Output: <class 'str'>
print(type(is_happy))      # Output: <class 'bool'>

# Type conversion examples

# String to Integer
age_text = "25"
age_number = int(age_text)
print(age_number + 5)        # Output: 30

# Integer to String
year = 2024
year_text = str(year)
print("Year is: " + year_text)  # Output: Year is: 2024

# Float to Integer (cuts off decimals!)
price = 99.99
print(int(price))           # Output: 99

# Integer to Float
count = 5
print(float(count))         # Output: 5.0

# String methods - text manipulation superpowers!

text = "  Hello World  "

# Convert to UPPERCASE
print(text.upper())           # Output: "  HELLO WORLD  "

# Convert to lowercase
print(text.lower())           # Output: "  hello world  "

# Remove spaces from both sides
print(text.strip())           # Output: "Hello World"

# Replace words
print(text.replace("World", "Python"))   # Output: "  Hello Python  "

# Split into a list of words
words = "apple,banana,cherry"
print(words.split(","))        # Output: ['apple', 'banana', 'cherry']

# Check if text contains something
print("World" in text)       # Output: True
print("Python" in text)      # Output: False

# Count occurrences
message = "I love Python. Python is great!"
print(message.count("Python"))  # Output: 2

# Get length of string
print(len("Hello"))          # Output: 5

word = "Python"

# Access single characters
print(word[0])       # Output: P (first character)
print(word[1])       # Output: y (second character)
print(word[-1])      # Output: n (last character)
print(word[-2])      # Output: o (second to last)

# Slicing - get a portion of the string
# syntax: word[start:stop] (stop is NOT included!)
print(word[0:3])     # Output: Pyt (characters 0, 1, 2)
print(word[2:])      # Output: thon (from position 2 to end)
print(word[:4])      # Output: Pyth (from start to position 3)
print(word[::2])     # Output: Pto (every 2nd character)
print(word[::-1])    # Output: nohtyP (reversed!)

# F-strings - the easiest way to insert variables into text!
# Put 'f' before the quotes, then use {variable} inside

name = "Alice"
age = 25
salary = 50000.789

# Simple f-string
print(f"My name is {name} and I am {age} years old.")
# Output: My name is Alice and I am 25 years old.

# Format numbers
print(f"My salary is ${salary:.2f}")  # .2f = 2 decimal places
# Output: My salary is $50000.79

# Do calculations inside {}
print(f"In 5 years I will be {age + 5}")
# Output: In 5 years I will be 30

# Comparison operators return True or False

print(5 == 5)      # Equal to? True
print(5 != 3)      # Not equal to? True
print(7 > 4)       # Greater than? True
print(2 < 8)       # Less than? True
print(6 >= 6)      # Greater than or equal? True
print(3 <= 5)      # Less than or equal? True

# Logical operators combine True/False values

age = 25
has_license = True

# AND - Both must be True
print(age >= 18 and has_license)    # True (can drive!)

# OR - At least one must be True
print(age < 18 or has_license)      # True (has license)

# NOT - Reverses the result
print(not has_license)               # False (opposite of True)

# Basic if statement
age = 20

if age >= 18:
    print("You are an adult!")
    print("You can vote!")

# Output:
# You are an adult!
# You can vote!

age = 15

if age >= 18:
    print("You are an adult!")
else:
    print("You are a minor.")

# Output: You are a minor.

# Grade calculator
score = 75

if score >= 90:
    print("Grade: A - Excellent!")
elif score >= 80:
    print("Grade: B - Good!")
elif score >= 70:
    print("Grade: C - Average")
elif score >= 60:
    print("Grade: D - Below Average")
else:
    print("Grade: F - Fail")

# Output: Grade: C - Average

# For loop - repeat for each item in a sequence

# Loop through a list
fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(f"I like {fruit}!")

# Output:
# I like apple!
# I like banana!
# I like cherry!

# range() generates a sequence of numbers

# Print numbers 0 to 4
for i in range(5):
    print(i)

# Output: 0, 1, 2, 3, 4

# Print numbers 1 to 5
for i in range(1, 6):
    print(i)

# Output: 1, 2, 3, 4, 5

# Print even numbers 0 to 10
for i in range(0, 11, 2):  # Start, Stop, Step
    print(i)

# Output: 0, 2, 4, 6, 8, 10

# While loop - repeat WHILE a condition is True

count = 1

while count <= 5:
    print(f"Count is: {count}")
    count = count + 1  # Don't forget to increment!

# Output:
# Count is: 1
# Count is: 2
# Count is: 3
# Count is: 4
# Count is: 5

# break - exit the loop immediately
for i in range(10):
    if i == 5:
        print("Found 5! Breaking out...")
        break
    print(i)

# Output: 0, 1, 2, 3, 4, Found 5! Breaking out...

# continue - skip this iteration, go to next
for i in range(5):
    if i == 2:
        continue  # Skip when i is 2
    print(i)

# Output: 0, 1, 3, 4 (skipped 2!)